Heart of the Alien is the sequel to Out of This World. The game continues directly where the original leaves off. Instead of controlling Lester, the player now controls his alien friend 'Buddy'. The game is very similar to the original with similar graphics, controls, story, and music. There are several flashback cut scenes in the game that allow players of the original Out of This World to see what'Buddy' was doing while Lester was fleeing.

It was only released for the Sega CD and without the original designers permission.